68 REPORTS ON INVESTIGATIONS AND PROJECTS. 



richest in the world, yet much material is needed before a reasonably com- 

 plete representation of the family can be presented. For the next two or 

 three years considerable time must be devoted to the task of collecting ma- 

 terial and organizing the collections. In the meantime, the work of describ- 

 ing and illustrating the better-known species will be carried on, and a fairly 

 good beginning has been made. 



Especial attention has been given by both Research Associates to the two 

 subfamilies Pereskioidea? and Opuntioidese, looking forward to the publica- 

 tion of the volume dealing with those groups as the first of the series to be 

 issued. 



Fruit Development in the Cactacecc, by D. S. Johnson. 



Dr. Johnson has undertaken a study of the morphological and physio- 

 logical features of the fruits of some of the cacti of the Tucson region 

 which present certain features of great importance in the phylogeny and 

 habit of these desert plants. During April, May, and June field studies were 

 made at the Desert Laboratory of a number of species and a fine series of 

 morphological material was accumulated to supplement the observations and 

 experimental results. Chief attention was paid to Opuntia fulgida, which 

 matures great numbers of greenish pear-shaped fruits with apparently per- 

 fect seeds. No seedlings have ever been found, however. The flowers open 

 in May. The fruits attain their mature size (20 by 30 mm.) in late summer. 

 Some of the fruits have only shriveled rudiments of ovules within, while 

 others have from a few to a hundred or more well-developed seeds with 

 curved, starch-filled embryos. The most interesting characteristic of these 

 fruits is their persistence on the parent plant for 10 or 12 or perhaps for 15 

 or 20 years. During this time the fruits continue to grow until they may 

 become 40 mm. in diameter and 70 or 75 mm. in length. This growth is due 

 chiefly to the activity of the general parenchyma, though the vascular bundles 

 increase six or eight times in cross-section area by the activity of the persist- 

 ent fascicular cambium. Cork is formed at and near the 15 to 40 leaf-scars 

 and over the top of the fruit. 



From a few or from as many as 15 or 20 of the dormant axillary buds of 

 this persistent fruit new flowers and then persistent fruits may arise in suc- 

 ceeding years. These newly formed fruits behave in like manner, so that in 

 10 or 12 years a parent fruit may have a cluster of scores or even hundreds 

 of daughter fruits depending from it. No evidence was found that the 

 seeds of these fruits ever germinate, though the seeds and their starch-filled 

 embryos remain apparently unchanged. Scores of very young plants were 

 examined and all were found to be evidently derived not from seeds, but by 

 the formation of roots and shoots from the dormant buds of fallen fruits or 

 vegetative joints. 



Some attention was paid incidentally to the color characters of Opuntia 

 versicolor, which shows a range from deep red to bright yellow within the 



